Biomedical subjects

X Xu

Publications and source records attributed to X Xu.

At least 433 records · Page 24Linked to original sources

PubMed1999

Distribution of disulfide bonds in the two-disulfide intermediates in the regeneration of bovine pancreatic ribonuclease A: further insights into the folding process.

The distribution of one-disulfide bonds in the two-disulfide intermediates in the oxidative refolding of bovine pancreatic ribonuclease A has been characterized. These two-disulfide intermediates were formed from the fully reduced denatured protein by oxidation with dithiothreitol, then blocked with AEMTS, purified by cation-exchange chromatography, enzymatically digested, and analyzed by reversed-phase high-performance liquid chromatography and mass spectrometry. The relative concentration of each of the 28 possible one-disulfide bonds in the two-disulfide ensemble was determined. Comparison with a statistical mechanical treatment of loop formation shows that the two-disulfide intermediates are probably compact. All 28 disulfide bonds were observed, demonstrating the absence of specific long-range interactions in these intermediates. Thermodynamic arguments suggest that the absence of such specific long-range interactions in the two-disulfide species may elevate the concentration of kinetically important three-disulfide intermediates and thereby increase the folding rate. Bond [65-72] was found to make up approximately 27% of the disulfide bonds of the two-disulfide species, significantly more than all other disulfides, because of stabilization by loop entropy factors and an energetically favorable beta-turn. This turn may be one of several chain-folding initiation sites, accelerating folding by decreasing the dimensionality of the conformational space that has to be searched.

Animals↗

PubMed1999

Crystal structures of

The crystal structures of [18]aneN(6)H(2)K[Co(CN)(6)].4H(2)O [potassium dihydrogen hexacyanocobaltate-1,4,7,10,13,16-hexaazacyclooctadecane-water (1/1/4)], [16]aneN(4)H(2)K[Co(CN)(6)] [potassium dihydrogen hexacyanocobaltate-1,5,9,13-tetraazacyclohexadecane (1/1)] and [12]aneN(4)H(3)[Co(CN)(6)].2H(2)O [trihydrogen hexacyanocobaltate-1,4,7,10-tetraazacyclododecane-water (1/1/2)] have been determined. For these supercomplexes, the [Co(CN)(6)](3-) binding with protonated polyammonium macrocycles is dominant in the binding competition between K(+) and [Co(CN)(6)](3-). It is suggested that the binding of [Co(CN)(6)](3-) with protonated polyammonium macrocycles is independent of the cavity size of the macrocycle, whereas that of K(+) is size-match selective. For [18]aneN(6)H(2)K[Co(CN)(6)].4H(2)O, the formation of a two-dimensional lamella may be derived from a chain-like arrangement of four-, five- and eight-membered rings in the network through the mutual balance between electrostatic and hydrogen-bonding interactions. [16]aneN(4)H(2)K[Co(CN)(6)] is a novel example demonstrating the anchoring of cobalticyanide through hydrogen-bonding interactions inside a zeolite-type cavity in the three-dimensional network formed by K(+) and the macrocycles through Coulombic interactions. Also, a three-dimensional network was formed mainly through hydrogen-bonding interactions between [Co(CN)(6)](3-), protonated macrocycles and water molecules in [12]aneN(4)H(3)[Co(CN)(6)].2H(2)O.

Journal Article↗

PubMed1999

[Investigations on dermal contamination among workers exposed to terephthalic acid].

Forty-three workers exposed to terephthalic acid(TPA) were selected to study the dermal contamination of TPA and the load of TPA in urine. The results showed that there existed a double logarithmic correlation between dermal contamination of TPA and air TPA concentration and a a logarithmic correlation between urinary TPA and total inhaled TPA. Neither dermal TPA contamination nor total TPA exposure exhibited and dose-dependent relationship with urinary TPA. Based on this occupational epidemiology investigation, it was proved that the absorption of TPA is not mainly from dermal exposure.

Adolescent↗

PubMed1999

Identification of RIP3, a RIP-like kinase that activates apoptosis and NFkappaB.

The tumor necrosis factor receptor 1 (TNFR1) and the Fas receptor recruit complexes formed by the interactions between RIP kinase, TRADD, FADD and RAIDD - adaptor proteins that contain death domains - which in turn recruit other proteins to initiate signaling [1][2][3][4][5]. To identify proteins associated with the TNF signaling pathway, we performed a yeast two-hybrid interaction screen using RIP as bait. We isolated a kinase, RIP3, which shares homology with the kinase domain of RIP and RIP2 (also known as Rick or CARDIAK). RIP3 could be co-immunoprecipitated with RIP, TRAF2 and TNFR1 in mammalian cells. The carboxy-terminal domain of RIP3, like that of RIP, could activate the transcription factor NFkappaB and induce apoptosis when expressed in mammalian cells. Interestingly, this region shares no significant sequence homology to the death domain of RIP, the caspase-recruiting domain (CARD) of RIP2 [6][7][8] or any other apoptosis-inducing domain. As with RIP and RIP2, the kinase domain of RIP3 was not required for either NFkappaB activation or apoptosis induction. Overexpression of a dominant-negative mutant of RIP3 strongly inhibited the caspase activation but not the NFkappaB activation induced by TNFalpha. Therefore, RIP3 appears to function as an intermediary in TNFalpha-induced apoptosis.

Apoptosis↗

PubMed1999

Activated protein kinase C isoforms target to cardiomyocyte caveolae : stimulation of local protein phosphorylation.

Protein kinase C (PKC) isoforms constitute an important component of the signal transduction pathway used by cardiomyocytes to respond to a variety of extracellular stimuli. Translocation to distinct intracellular sites represents an essential step in the activation of PKC isoforms, presumably as a prerequisite for stable access to substrate. Caveolae are specialized subdomains of the plasma membrane that are reported to concentrate key signaling proteins and may represent a locus for PKC action, given that PKC activators have been reported to dramatically alter caveolae morphology. Accordingly, this study examines whether PKC isoforms initiate signaling in cardiomyocyte caveolae. Phorbol ester-sensitive PKC isoforms were detected at very low levels in caveolae fractions prepared from unstimulated cardiomyocytes; phorbol 12-myristate 13-acetate (PMA) (but not 4alpha-PMA, which does not activate PKC) recruited calcium-sensitive PKCalpha and novel PKCdelta and PKCepsilon to this compartment. The subcellular localization of the phorbol ester-insensitive PKClambda isoform was not influenced by PMA. Endothelin also induced the selective translocation of PKCalpha and PKCepsilon (but not PKCdelta or PKClambda) to caveolae. Multiple components of the extracellular signal-regulated protein kinase (ERK) cascade, including A-Raf, c-Raf-1, mitogen-activated protein kinase kinase, and ERK, were detected in caveolae under resting conditions. Although levels of these proteins were not altered by PMA, translocation of phorbol ester-sensitive PKC isoforms to caveolae was associated with the activation of a local ERK cascade as well as the phosphorylation of a approximately 36-kDa substrate protein in this fraction. Finally, a minor fraction of a protein that has been designated as a receptor for activated protein kinase C resides in caveolae and (along with caveolin-3) could represent a mechanism to target PKC isoforms to cardiomyocyte caveolae. These studies identify cardiomyocyte caveolae as a meeting place for activated PKC isoforms and their downstream target substrates.

Animals↗

PubMed1999

Murine fibroblast growth factor receptor 1alpha isoforms mediate node regression and are essential for posterior mesoderm development.

Alternative splicing in the fibroblast growth factor receptor 1 (Fgfr1) locus generates a variety of splicing isoforms, including FGFR1alpha isoforms, which contain three immunoglobulin-like loops in the extracellular domain of the receptor. It has been previously shown that embryos carrying targeted disruptions of all major isoforms die during gastrulation, displaying severe growth retardation and defective mesodermal structures. Here we selectively disrupted the FGFR1alpha isoforms and found that they play an essential role in posterior mesoderm formation during gastrulation. We show that the mutant embryos lack caudal somites, develop spina bifida, and die at 9.5-12.5 days of embryonic development because they are unable to establish embryonic circulation. The primary defect is a failure of axial mesoderm cell migration toward the posterior portions of the embryos during gastrulation, as revealed by regional marker analysis and DiI labeling. In contrast, the anterior migration of the notochord is unaffected and the embryonic structures rostral to the forelimb are relatively normal. These data demonstrate that FGF/FGFR1alpha signals are posteriorizing factors that control node regression and posterior embryonic development.

Abnormalities, Multiple↗

PubMed1999

[Rapid detection of non-deletional alpha-thalassemia mutations by PCR-LIS-SSCP]

OBJECTIVE: To establish a rapid and convenient single strand conformation polymorphism (SSCP) analysis method for detecting the point mutation of non-deletional alpha-thalassemia. METHODS: The 543bp DNA fragment spanning the hot spot region mainly responsible for non-deletional alpha-thalassemia was nested amplified using the selective amplification of alpha2 globin gene as a template and was denatured with low ionic strength(LIS) solution followed by SSCP analysis. RESULTS: LIS buffer was more efficient for ssDNA formation than formamide buffer was and the formation of ssDNA was very stable. In addition to a normal electrophoresis pattern, at least three SSCP profiles can be detected by the present method when the DNA samples bearing non-deletional genes of Hb H disease were screened. Confirmed by DNA sequencing analysis, the DNAs represented these profiles have turned out to be the different three mutants, i.e., the alphaCS mutation, the alpha QS mutation and the alphaWestmead mutation, respectively. Only 3 hours were needed to complete the electrophoresis procedure of this method. CONCLUSION: PCR-LIS-SSCP can be used as a tool in rapid screening for the alterations in human alpha-globin gene.

Journal Article↗

PubMed1999

[Study on the relationship between the structure of chlorobenzenes and their toxicity to guppy].

The quantum chemical indexes of 12 chlorobenzenes were calculated by CNDO/2 method. Quantitative structure-activity relationship between the quantum chemical indexes of chlorobenzenes and their toxicity to Guppy was calculated by step regression analysis. The linear correlation equation is as follows: DLC50 = -0.15 + 6.865 sigma QR, n = 12, R = 0.9867 s = 0.15, F = 367.64. Results showed that the toxicity of chlorobenzenes to the aquatic Guppy are increased as the increase of their ability to accept electrons.

Animals↗

PubMed1999

Two multiplex PCR-based DNA assays for the thrombosis risk factors prothrombin G20210A and coagulation factor V G1691A polymorphisms.

Two coagulation factor polymorphisms, G1691A in the factor V gene and G20210A in the prothrombin gene, are currently the most common known genetic risk factors for venous thrombosis in caucasian populations. Experimental conditions that permit simultaneous determination of these two polymorphisms using PCR-based DNA assays with the restriction enzyme, Hind III, were developed. Moreover, novel PCR-based DNA assays were established using primers that introduce specific cleavage sequences which then permit the simultaneous determination of these polymorphisms using Sac I restriction digestion analysis. Multiplex PCR-based DNA assays were used to analyze a family with a history of venous thrombosis in which these polymorphisms were both present and the results confirm the interesting variability of these genetic risk factors among family members who are symptomatic.

Biological Assay↗

PubMed1999

Familial aggregation of blood pressure in a rural Chinese community.

This study investigated blood pressure in 1,183 Chinese nuclear families (mother, father, and first two children) via a cross-sectional 1994-1997 survey. The mother's, the father's, and the first sibling's blood pressures were each significantly and independently related to the second sibling's blood pressure after adjustment for sex, age, height, weight, education, smoking, and alcohol consumption. The association was consistent across the four age strata (6-10, 11-14, 15-19, and > or = 20 years). The rate of high systolic blood pressure in the second sibling was lowest (2.3%) when both parents and the first sibling were in the low blood pressure tertile (low-low group) and highest (26.0%) when these family members were in the high blood pressure tertile (high-high group). The rate was intermediate if only the parents (10.7%, high-low group) or the first sibling (8.4%, low-high group) was in the high blood pressure tertile. As compared with the low-low group, the odds ratios for the high-high, high-low, and low-high groups were 14.3 (95% confidence interval 4.3-48.2), 4.3 (95% confidence interval 1.2-15.6), and 3.9 (95% confidence interval 1.1-14.4), respectively. A similar pattern was found for diastolic blood pressure. The data indicate a strong familial aggregation of blood pressure in this population and show that such a familial influence on blood pressure can be detected from early childhood onward.

Adolescent↗

PubMed1999

Rapid death of adoptively transferred T cells in acquired immunodeficiency syndrome.

Human immunodeficiency virus (HIV)-specific cytotoxic T lymphocytes (CTL) probably play the major role in controlling HIV replication. However, the value of adoptive transfer of HIV-specific CTL expanded in vitro to HIV+ patients has been limited: this contrasts with the success of CTL therapy in treating or preventing Epstein-Barr virus and cytomegalovirus disease after bone marrow transplantation (BMT). We investigated the fate of expanded HIV-specific CTL clones in vivo following adoptive transfer to a patient with acquired immunodeficiency syndrome (AIDS). Two autologous CTL clones specific for HIV Gag and Pol were expanded to large numbers (>10(9)) in vitro and infused into an HIV-infected patient whose viral load was rising despite antiretroviral therapy. The fate of one clone was monitored by staining peripheral blood mononuclear cells (PBMCs) with T-cell receptor-specific tetrameric major histocompatibility complex (MHC)-peptide complexes. Although the CTL transfer was well tolerated, there were no significant changes in CD4 and CD8 lymphocyte counts and virus load. By tracking an infused clone using soluble MHC-peptide complexes, we show that cells bearing the Gag-specific T-cell receptors were rapidly eliminated within hours of infusion through apoptosis. Thus, the failure of adoptively transferred HIV-specific CTL to reduce virus load in AIDS may be due to rapid apoptosis of the infused cells, triggered by a number of potential mechanisms. Further trials of adoptive transfer of CTL should take into account the susceptibility of infused cells to in vivo apoptosis.

Adoptive Transfer↗

PubMed1999

[Rapid detection of an HPFH deletion by PCR amplification with three primers bridging the breakpoint].

OBJECTIVE: To establish a rapid and reliable PCR method for detecting a deletional hereditary persistence of fetal hemoglobin (HPFH) found in Chinese. METHODS: Based on some novel DNA sequences across the 3'breakpoint of a HPFH deletion observed in our laboratory, we designed a PCR amplification with three primers bridging the breakpoint. In this system, oligonucleotide primers have been chosen which allow specific identification of both normal and deletional chromosomes under identical condition in either the same or parallel PCR reactions. RESULTS: The expected two specific amplification bands were produced; one was 565bp in length and stood for the normal alleles,the other,37bp in length represented the mutant alleles of beta-globin gene cluster. This duplex system could directly genotype DNA samples bearing this type of HPFH deletion. CONCLUSION: This rapid and inexpensive method could be used as a routine method in the molecular screening of carriers and for the prenatal diagnosis of this disease.

Base Sequence↗

PubMed1999

RGS proteins determine signaling specificity of Gq-coupled receptors.

Regulators of G protein signaling (RGS) proteins accelerate GTP hydrolysis by Galpha subunits, thereby attenuating signaling. RGS4 is a GTPase-activating protein for Gi and Gq class alpha subunits. In the present study, we used knockouts of Gq class genes in mice to evaluate the potency and selectivity of RGS4 in modulating Ca2+ signaling transduced by different Gq-coupled receptors. RGS4 inhibited phospholipase C activity and Ca2+ signaling in a receptor-selective manner in both permeabilized cells and cells dialyzed with RGS4 through a patch pipette. Receptor-dependent inhibition of Ca2+ signaling by RGS4 was observed in acini prepared from the rat and mouse pancreas. The response of mouse pancreatic acini to carbachol was about 4- and 33-fold more sensitive to RGS4 than that of bombesin and cholecystokinin (CCK), respectively. RGS1 and RGS16 were also potent inhibitors of Gq-dependent Ca2+ signaling and acted in a receptor-selective manner. RGS1 showed approximately 1000-fold higher potency in inhibiting carbachol than CCK-dependent signaling. RGS16 was as effective as RGS1 in inhibiting carbachol-dependent signaling but only partially inhibited the response to CCK. By contrast, RGS2 inhibited the response to carbachol and CCK with equal potency. The same pattern of receptor-selective inhibition by RGS4 was observed in acinar cells from wild type and several single and double Gq class knockout mice. Thus, these receptors appear to couple Gq class alpha subunit isotypes equally. Difference in receptor selectivity of RGS proteins action indicates that regulatory specificity is conferred by interaction of RGS proteins with receptor complexes.

Animals↗

PubMed1999

Correlation between expression of peroxisome proliferator-activated receptor beta and squamous differentiation in epidermal and tracheobronchial epithelial cells.

Previously, several members of the nuclear receptor superfamily have been implicated in the regulation of epidermal differentiation. In this study, we analyze the expression of members of the PPAR nuclear receptor subfamily in relation to the process of squamous differentiation in normal human epidermal keratinocytes (NHEK), human tracheobronchial epithelial (HBE) cells and the epidermis in vivo. Our results demonstrate that induction of differentiation in NHEK by either treatment with the phorbol ester phorbol 12-myristate-13-acetate (PMA), suspension culture or confluence greatly enhances the expression of PPARbeta mRNA. Likewise, topical treatment of mouse skin with PMA results in increased PPARbeta mRNA expression in the epidermis. In addition, the induction of squamous differentiation in HBE cells was also associated with an upregulation of PPARbeta mRNA expression. Finally, in situ hybridization analysis localized PPARbeta mRNA to the suprabasal layers of normal human skin. Our results demonstrate that the expression of PPARbeta is associated with squamous differentiation suggesting a regulatory role for this receptor in the control of specific genes during this differentiation process.

Animals↗

PubMed1999

Sperm aneuploidy among Chinese pesticide factory workers: scoring by the FISH method.

BACKGROUND: A study of the prevalence of sperm aneuploidy among pesticide factory workers was conducted in Anhui, China. METHODS: We recruited 75 men: 32 subjects from a large pesticide-manufacturing plant and 43 subjects from a nearby textile factory free of pesticide exposure. Each subject met the following criteria: age of 20-40 years; continuous work in the plant for 3 months prior to the study, no congenital anomalies or acquired disease of the external genitalia and no history of recent febrile illness or mumps. Within one hour after collection from each subject, semen was evaluated in terms of several parameters and smear slides were prepared. RESULTS: Exposure assessment revealed that workers in the pesticide plant were exposed to ethyl parathion or methamidophos, each of which is a potent organophosphate pesticide, at a median level of 0.02 mg/m3 (8-hour time weighted average as measured by personal pump) while workers in the control plant had no such occupational exposure. Twenty-nine semen slides (13 from the exposed group and 16 from the unexposed group) were randomly chosen for aneuploidy scoring by the three-color fluorescence in situ hybridization (FISH) method with scorers being unaware of exposure status. Median semen parameters were as follows for exposed (and unexposed) men: abstinence period, 3 days (4 days); sperm concentration, 52.8x10(6)/ml (53.1x10(6)/ml); proportion of sperm with normal motility, 50.5% (61.3%); and proportion of sperm with normal morphology, 59% (61.5%). The specific chromosome abnormalities of interest were disomy for chromosome 18 and the three different types of sex chromosome disomy (i.e. XX, XY, YY disomy). The crude proportion of all aneuploidy combined was 0.30% and 0.19% for sperm from exposed and unexposed men, respectively. Poisson regression with overdispersion adjustment yielded significantly different crude risks of aneuploidy - 3.03 and 1.94 per 1,000 sperm from exposed and unexposed men, respectively - giving a rate ratio of 1.56 (95% CI, 1.06-2.31). The regression coefficients remained statistically significant after adjustment for inter-technician variability giving a rate ratio of 1.51 (95% CI, 1. 04-2.20). CONCLUSIONS: We conclude that occupational exposure to organophosphate pesticides moderately increases the prevalence of sperm aneuploidy.

Adult↗

PubMed1999

Paraoxonase polymorphism and its effect on male reproductive outcomes among Chinese pesticide factory workers.

BACKGROUND: Serum paraoxonase has been associated with the metabolism of organophosphate pesticides in humans. Molecular analysis of the human paraoxonase gene (PON1) has revealed that Arg192 homozygotes have a greater detoxifying capability than Gln192 homozygotes. We examined the effects of PON1 genotypes on male reproductive outcomes and its interaction with exposure to organophosphate pesticides. METHODS: We studied 60 Chinese pesticide-factory workers and 89 textile-factory workers who were unexposed to pesticides. The respective allele frequencies of Arg192 and Gln192 were 0.62 and 0.38. Pesticide exposure among 36 exposed subjects and 12 unexposed subjects, regardless of gender, was assessed by personal measurement of pesticide residues over an entire 8-hr shift and measurement of urinary p-nitrophenol level over a 24-hr period. We analyzed semen and hormone data collected from male subjects. RESULTS: When the three PON1 genotypes were analyzed separately, a gene dose effect was not detected. We used the unexposed Arg192 homo/heterozygotes as the reference group, and re-analyzed the data. Exposed Arg192 homo/heterozygotes had significantly lower sperm count (chi 2 = 9.01, P < 0.01) and lower percentage of sperm with normal morphology (chi 2 = 4.18, P < 0.05) than the reference group. Both unexposed Gln192 homozygotes (chi 2 = 4.90, P < 0.05) and exposed Arg192 homo/heterozygotes (chi 2 = 10.00, P < 0.01) showed significantly lower sperm concentrations than the reference group. In addition, exposed Arg192 homo/heterozygotes had significantly higher serum LH levels (chi 2 = 7.94, P < 0.01) than the reference group. CONCLUSIONS: Because of a small sample size, our findings are highly preliminary. Nevertheless, it calls for further investigation of the interaction between the PON1 genotype and organophosphate pesticide exposure on male reproductive outcomes.

Adult↗

PubMed1999

A genome-wide scan for a simulated data set using two newly developed methods.

A genome-wide scan of a simulated data set for fictitious disease genes was conducted using both semiparametric and nonparametric methods. The semiparametric model-based method, which tests for linkage/linkage disequilibrium separately and together, correctly identified all three underlying disease loci along with two false positives through the linkage analysis. However, the nonparametric model-free method which tests combined linkage/linkage disequilibrium, failed to yield any results due to the lack of linkage disequilibrium information in the data.

Chromosome Mapping↗

PubMed1999

Role of Salmonella enterotoxin in overall virulence of the organism.

In this study, the Salmonella enterotoxin gene (stn) was mutated by marker exchange mutagenesis, and the overall virulence of the organism was evaluated. Salmonella marker exchange mutants evoked significantly less fluid secretion in mouse intestinal loops compared to that seen with wild-type S. typhimurium. Salmonella mutants were as invasive as wild-type bacteria for HeLa cells; however, their capacity to cause destruction of the intestinal mucosa was impaired, when compared with wild-type bacteria by electron microscopy. Upon oral challenge of mice, the LD(50)of the Salmonella mutants was greater than that for the wild-type bacteria. The fluid secretory potential, as well as a reduction in the LD(50)of these mutants was restored when the mutated stn gene was replaced by the native stn gene sequence. These mutations had no effect on the aerobic growth of these bacteria in minimal or complete medium; anaerobic growth was also not affected. With these studies, we demonstrated that the presence of an intact stn gene contributed significantly to the overall virulence of S. typhimurium in a murine model.

Animals↗